The present invention relates to a rotation signal detection device of a DC motor with brushes which may be used for controlling a reel motor of a tape recorder or the like.
A magnetic tape of the tape recorder is wound around reels and these reels are driven by a reel motor, thus winding the magnetic tape from one reel to the other. When the magnetic tape accidentally becomes wound around a capstan or the like while the magnetic tape is traveling, smooth tape travel is prevented which causes cutting of the tape, reel motor troubles or the like. In this case, the power to the reel motor must be immediately stopped. The magnetic tape stops traveling when the tape is wound to the end. The reel motor must then be turned off or the motor rotation must be reversed. For these purposes, the rotation of the reel motor must be supervised and the driving circuit of the reel motor must be controlled in response to a rotating condition detecting signal. Further, tone quality of the sound reproduced by the tape recorder greatly depends on the tape traveling speed. If the rotation of the reel motor is unstable, the sound quality is degraded. In order to stabilize the tape traveling speed, a tension servo circuit has been used to control the rotation of the reel motor.
For controlling the reel motor rotation described above, the rotating condition of the reel motor must be detected. Conventionally, a combination of a magnet and a lead switch or a Hall element is utilized for detecting the rotating condition magnetically. Alternatively, a photocoupler is utilized for detecting the rotating condition photoelectrically.
These rotation detecting circuits, however, are supplementarily added to the tape recorder as a special detecting element, so the overall structure of the tape recorder becomes complex, thus adversely increasing the manufacturing cost.